The present invention is related to the field of data communications in the local access loop of the telephone network. In particular, a system and method are disclosed for providing high-speed data and voice services over standard twisted-pair voice-lines in a digital loop carrier (xe2x80x9cDLCxe2x80x9d) system.
In a typical DLC system, the digital transport capabilities of the phone network are extended from the central office switch into a particular neighborhood or business location. A remote digital terminal (xe2x80x9cRDTxe2x80x9d) is placed at a remote location from the central office and is connected to it via a fiber-optic cable, or some other high-bandwidth connection. The remote digital terminal receives PCM-modulated voice information from the central office switch, converts the digital PCM signals into analog voice signals, and routes the analog voice signals to a particular customer location via a plurality of line-cards that connect the RDT to the customer""s location. Similarly, the RDT converts analog voice information from the customer to a digital PCM format for transport back to the central office switch. An example of a digital loop carrier system is set forth in U.S. Pat. No. 5,046,067 (xe2x80x9cthe ""067 patentxe2x80x9d), which is assigned to the assignee of the present invention. The teaching of this patent is hereby incorporated into the present application by reference.
The RDT typically includes an interface terminal for communicating with the central office over the fiber-optic connection, a common equipment shelf for housing equipment that is capable of exchanging PCM voice signals with a digital switch at the central office and that can also demultiplex high-bandwidth signals (such as DS-1 signals) into lower-bandwidth signals (such as DS-0) signals, and a plurality of copper shelves for housing line-cards (also known as channel units). The line-cards convert the PCM digital voice signals from the common equipment shelf into analog signals, and vice versa, for each customer that is connected to the RDT.
Dial-up Internet access is a presently available technique for transporting data to local customers. This mode of data communication transmits digital data over an analog voice line using a low-frequency (voice range) modem. Presently, the highest-bandwidth that such modems are capable of communicating is about 53 Kbps. This is not sufficient for many Internet applications, such as video-conferencing, interactive gaming, large file downloads, etc.
Another presently available technique for transporting data to a local user is via a dedicated digital line, such as a T-1 line, or an ISDN line. Although these alternatives provide higher-bandwidth capabilities than an analog modem, they are very costly to the average consumer, and therefore have met with minimal market penetration.
Recently, a series of new techniques for transporting data over voice lines, known as digital subscriber line (or DSL) have been proposed. DSL technologies use advanced digital modulation schemes to transport orders-of-magnitude more information over copper phone lines than analog modems or ISDN lines. The primary mechanisms for achieving such high throughput are higher-frequency transmission and advanced modulation schemes. Because of the promise of higher transport speeds, DSL is very desirable for Internet applications. In addition, DSL technology should be available at a fraction of the cost of dedicated T-1 lines, since no dedicated link is required.
Regardless of what DSL technique is implemented, problems exists with integrating DSL technology into existing digital loop carrier systems. Power is a primary concern. Typical DSL technologies require 4-8 watts per line-card to operate the complicated modulation algorithms, thus limiting their applicability to existing DLC installations, which are power-limited. Limited range is another concern. Some customers are at significant distances from the RDT, and if the DSL line-card range is limited, then additional hardware may be required to connect to a particular customer that is far from the RDT. Noise introduced into the system is yet another concern. But perhaps the most vexing problem is how to adapt the existing DLC infrastructure to support high-bandwidth digital data without reducing the voice-bandwidth capabilities of the system, or without having to replace the RDT equipment already installed in the field. The present invention solves this problem, as well as many others.
Thus, there remains a general need in this field for a system and method for integrating DSL capabilities into existing DLC systems.
There remains a more particular need for such a system and method in which an auxiliary bus is converted into a digital data bus for transporting data directly between the interface terminal and the DSL line-cards in the RDT, thereby bypassing the common equipment shelf and minimizing the impact to the voice-carrying capabilities of the DLC system.
There remains an additional need for such a system and method in which multiple digital signals from the DSL line-cards are switched at the RDT, prior to transmission to the central office switch.
There remains yet another need in this field for a combination voice/DSL line-card for use in a DLC system.
There remains still another need for such a combination voice/DSL line-card that utilizes low-power modulation technology, such as quadrature-phase shift keying (xe2x80x9cQPSKxe2x80x9d).
The present invention overcomes the problems noted above and satisfies the needs in this field for a digital loop carrier system that is capable of transporting both voice and DSL data signals. The digital loop carrier system includes a remote digital terminal having an interface terminal, a common equipment shelf for interfacing digital voice signals to the central office switch, and at least one copper shelf coupled to the common shelf for holding voice line-cards that convert digital voice signals into analog voice signals (and vice versa) for transport to customer premises. At least one copper shelf is configured to include an auxiliary digital data bus (preferably a packet data bus) for connecting combination voice/DSL line-cards and at least one data uplink card. The data uplink card is coupled directly to the interface terminal-to enable DSL data transport without impacting digital voice capabilities through the common equipment. Also disclosed is an optional Ethernet switch in the remote digital terminal for concentrating multiple DSL signals prior to transport back to the central office.
As described in more detail below, the present invention can be used with any DSL modulation scheme. However, because of the inherent power limitations of existing DLC installations, the preferred embodiment of the present invention utilizes a low-power QPSK-modulation technique. It is to be understood that this is only one example of the many types of modulation schemes that could be integrated into the combination voice/DSL line-cards, and the overall system of the present invention.
One embodiment of the present invention provides a system for transporting voice and digital subscriber line (DSL) data in the local telephone loop, comprising: (a) a central office switch coupled to voice and data sources; (b) a plurality of customer interface devices; and (c) a remote digital terminal (RDT) coupled between the central office switch and the customer interface devices, comprising: (1) an interface terminal for communicating voice and data signals between the central office switch and the RDT; (2) a common equipment shelf coupled to the interface terminal for transmitting and receiving voice signals; and (3) at least one copper equipment shelf coupled to the common equipment shelf, the copper equipment shelf including a plurality of communication cards and a digital data bus for transporting data between the cards, wherein one of the communication cards is a data uplink card coupled to the interface terminal for transmitting and receiving data signals, and another one of the communication cards is a combination voice/DSL card for transmitting voice and data signals between at least one of the customer interface devices and the RDT.
Another embodiment of the present invention provides a method of transporting voice and data in a digital loop carrier system, comprising the steps of providing a remote digital terminal in communication with a central office switch and a plurality of customer interface devices, the remote digital terminal having a interface terminal, at least one common equipment shelf, and at least one copper shelf, receiving voice and data information from the central office switch at the interface terminal; routing the voice information through the common equipment shelf and the copper shelf to the plurality of customer interface devices; and routing the data information directly to the copper shelf and then onto the plurality of customer interface devices.
Another embodiment of the present invention provides a remote digital terminal for use in a digital loop carrier system, comprising: an interface terminal; a common equipment shelf coupled to the interface terminal; a copper equipment shelf coupled to the common equipment shelf, including: at least one combination voice/DSL line-card; at least one data uplink card coupled to the interface terminal; and a digital packet data bus; wherein voice signals are routed from the interface terminal to the common equipment shelf and then to the combination voice/DSL line-card, and data signals are routed from the interface terminal to the data uplink card and then to the combination voice/DSL line-card.
The present invention also provides an improved digital loop carrier system including a remote digital terminal having an interface terminal, at least one common equipment shelf for interfacing voice signals to a central office switch via the interface terminal, and at least one copper shelf coupled to the common shelf for housing line-cards that convert digital voice signals into analog voice signals for transport to customer locations, the improvement comprising: at least one combination voice/DSL line-card housed in the copper shelf for communicating voice and data signals to a customer location; at least one data uplink line-card housed in the copper shelf for communicating data signals to the combination voice/DSL line-card; and a digital data bus for connecting the combination voice/DSL line-card to the data uplink line-card.
Another embodiment of the present invention provides a remote digital terminal for transporting voice and data signals between a central office switch and a plurality of customer premises, comprising: a plurality of combination voice/DSL line-cards for transporting voice and data signals to a customer premises; means for routing voice signals from the central office switch to the plurality of combination voice/DSL line-cards; and means, separate from the means for routing voice signals, for routing data signals from the central office switch to the plurality of combination voice/DSL line-cards.
The present invention also provides a novel combination voice/DSL line-card. One embodiment of this combination voice/DSL line-card includes: a PCM voice signal interface; voice-frequency channel circuitry coupled to the PCM voice signal interface for transporting voice signals; a digital data bus interface; and DSL channel circuitry coupled to the digital data bus interface for transporting data signals.
Another embodiment of the voice/DSL line-card includes: means for receiving digital PCM voice signals; means for converting the digital PCM voice signals into analog voice signals; means for receiving digital data signals; and means for converting the digital data signals into DSL-modulated data signals. These are just some of the embodiments of the present invention described in more detail below in connection with the drawing figures. Other embodiments not specifically disclosed or described would be apparent to one of ordinary skill in this art.
The present invention provides many advantages over presently available techniques for transporting voice and digital data in the local loop, particularly when applied to DSL transport over existing DLC systems. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) existing DLC systems can be easily and cost-effectively upgraded to the present invention; (2) the preferred QPSK modulation scheme provides low power in comparison to other presently known DSL techniques; (3) voice and data services are combined on a single line-card; (4) DSL data services can be added or designed-into a DLC system without impacting the voice carrying capabilities of the system; (5) DSL data can be combined at the RDT prior to transmission to the central office switch; and (6) different types of DSL technologies can be integrated into the same DLC system.
These are just a few of the many advantages of the present invention, as described in more detail below. As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiments set forth below are to be regarded as illustrative in nature and not restrictive.